The purpose of research carried out is to model the proposed route of prostaglandin (PG) biosynthesis. One mechanism proposed for PG biosynthesis involves the free radical cyclization of an unsaturated peroxy radical to form a bicyclic endoperoxide (PGG & PGH). Our approach to modeling PG biosynthesis is to use unsaturated hydroperoxides as the source of the corresponding peroxy radical. For example, incubation of unsaturated hydroperoxides with DBPO (a free radical initiator) leads to products which appear to be the result of abstraction of the labile hydroperoxy hydrogen to form the peroxy radical. The peroxy radical so formed undergoes cyclization to produce endoperoxides. Unsaturated hydroperoxides have been prepared which should be analogs for PG biosynthesis. These hydroperoxides are prepared by the action of soybean lipoxidase on gamma-linolenic acid. Incubation of these hydroperoxides with DBPO followed by NaBH4 reduction leads to products which are analogs of PGF l alpha. Work in progress now involves the estimation of PG yields obtained and the identification of other products formed in peroxy radical cyclizations.